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The present invention relates to ultrasonic receiver arrays for use in imaging ultrasonic devices and, in particular, to an improved method of providing electrical connection for such receiver arrays.
Ultrasound may be used to characterize living tissue through the attenuation, change in speed of sound, or other modification of ultrasonic energy through the tissue. A device using this approach for quantitative measurement of bone quality, such as may be useful in the study and treatment of osteoporosis, provides an ultrasonic transmitter positioned across from an ultrasonic receiver about a volume which may receive a portion of the body containing bone with high trabecular content. A convenient site for such a measurement is the os calcis of the human heel, which includes substantial trabecular bone structure and minimal intervening soft tissue.
It can be desirable to combine the capability of imaging and quantitative measurement to an ultrasonic device, for example, to allow the operator to ensure correct foot location and thus improve repeatability in measurements taken at different times. U.S. Pat. No. 6,027,449, entitled: xe2x80x9cUltrasonometer Employing Distensible Membranesxe2x80x9d, assigned to the assignee of the present case and hereby incorporated by reference, describes a method of manufacturing an ultrasound detection array using a thin film of piezoelectric material plated with regularly spaced electrodes. The electrodes are attached to processing circuitry using acoustically transparent Mylar connectors. Such connectors provide extremely high quality connection with minimal acoustic disruption, but can be difficult to manufacture. What is needed is an alternative connection method that provides high reliability, linearity, and stability.
The present invention provides a contact system for film-type piezoelectric material permitting simplified manufacturing. The piezoelectric film is supported on its front face by an acoustically transparent material and a set of springs are sandwiched between the rear face of the piezoelectric film and a circuit board having processing circuitry, to provide electrical connection therebetween. The springs may be pre-assembled in a carrier by vibratory or other automatic assembly techniques and provide for high areal density interconnection with moderate effect on the acoustic signal.
Specifically, the present invention provides an ultrasonic array using a piezoelectric sheet having a plurality of electrodes spaced at predetermined array locations on a rear surface of the sheet. A set of electrically independent conductive springs are positioned at the array locations and a circuit card having electrical terminals positioned at the array location on a front side of the circuit card, is placed proximate thereto. A retention frame compresses the array of conductive springs between the piezoelectric sheet and the circuit card to establish electrical communication between the electrodes and terminals.
In this way, an acoustically light and readily manufactured connection is made.
An acoustically transparent support block may be fastened to a front surface of the piezoelectric material. This block allows the thin film piezoelectric material to resist the pressure of the springs. The block may further provide for impedance matching from water coupling material to the piezoelectric film. In this regard, the support block may have an acoustic impedance between the acoustic impedance of the piezoelectric sheet and the acoustic impedance of water.
The circuit card may include at least one multiplexer circuit on the second side of the circuit card opposite the terminals but communicating with the terminals and for selectively collecting at least one communication lead to ones of the terminals.
In this way, the high density of connections may be converted to a convenient number of leads and the circuitry for doing so may be displaced from acoustic contact with the piezoelectric film.
The device may include a spring support plate positioned between the film and the circuit card having a series of axial holes sized to support the springs in position at the array locations. A means for maintaining an air gap positioned between the spring support plate and the film may be provided.
In this way, the springs may be supported to improve manufacturability of the device without interfering with the acoustic properties of the connection.
The array locations may be interstices of a rectangular grid separated by less than one-half centimeter.
Thus, the present invention can provide extremely high connection densities.
The foregoing features and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose.